Hematological support techniques which may be of importance in the treatment of patients with cancer or aplastic anemia are being developed and improved. Studies in patients and in pre-clinical canine models facilitate the development of new methods for the cryopreservation of human marrow, permit a determination of the dose of stem cells which is necessary for bone marrow reconstitution following ablative chemotherapy, and have led to the collection of adequate numbers of stem cells from peripheral blood for autologous reconstitution using automated cell separators. In the area of granulocyte transfusion, we have established the dose of granulocytes necessary to protect an animal from life-threatening pseudomonas sepsis, and are studying ways of achieving this dose in man. Clinical and in vitro studies are being utilized to clarify which histocompatibility antigens are of the greatest importance and in the identification of compatible donor-recipient pairs for the purpose of platelet transfusion.